Heat Transfer Tubes, Combustion Gas Eductors, And Cooking Medium Heating Systems Including Such Tubes And Eductors

ABSTRACT

A cooking medium heating system includes a cooking vessel for holding a cooking medium, at least one heat transfer tube for transferring heat generated by combustion to the cooking medium, and a combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening. Each heat transfer tube includes a bottom wall, a pair of side walls, a top wall, and a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof. The tubes may include at least one heat transfer fin and a combustion gas flow separator dividing the tube into two spaces between the separator and the pair of side walls. The combustion gas eductor includes a flue including a narrower, exhaust gas receiving end disposed adjacent to the combustion gas exhaust opening, a nozzle including a nozzle inlet and a nozzle outlet, and a blower.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/055,415, filed May 22, 2008, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to heat transfer tubes for transferring heat from combustion gases to a cooking medium. In particular, the present invention is directed towards heat transfer tubes comprising internal heat transfer fins or a separator for directing the combustion gasses against the walls of such heat transfer tubes, or both. The present invention also relates generally to eductors for venting combustion gas exhausted from such heat transfer tubes. In addition, the present invention relates generally to cooking medium heating systems for heating a cooking medium in a cooking vessel having such heat transfer tubes passing therethrough.

2. Description of Related Art

Known fryers, e.g., open-well fryers and pressure fryers, are used to cook various food products, e.g., poultry, fish, or potato products. Such fryers include a cooking vessel, e.g., a fry pot or vat, and the cooking vessel is filled with a cooking medium, e.g., an oil, a liquid shortening, a meltable-solid shortening, or water. Such fryers also include a heating element, e.g., an electrical heating element, such as a heating coil, or a gas heating element, such as a gas burner and gas conveying tubes, which heat the cooking medium in the cooking vessel. After the cooking medium reaches a preset cooking temperature, the food product is placed into the cooking medium, such that the food product is cooked in the cooking medium. For example, the food product may be positioned inside a container, e.g., a wire basket, and submerged in the cooking medium for a predetermined amount of time sufficient to cook the food product. The cooking medium is used during several cooking cycles before the cooking medium inside the cooking vessel is replaced or is supplemented with a new or filtered supply of cooking medium.

Because health benefits may be achieved by avoiding foods containing transfats, food preparers recently have sought to reduce or eliminate the amount of transfats present in cooking medium. Transfat is a common name for a type of unsaturated fat with trans-isomer fatty acid(s). Transfats may be monounsaturated or polyunsaturated fats. Many transfats consumed today are created by partially hydrogenating plant oils, by which hydrogen atoms are added to unsaturated fats, making them more saturated. These more saturated fats may have higher melting points, which has made them attractive for baking and extends their shelf-life. Unlike other dietary fats, transfats do not appear to be either essential or beneficial. Moreover, consumption of tranfats may increase the risk of developing coronary heart disease by raising levels of LDL cholesterol and lowering levels of HDL cholesterol. Some health authorities recommend reduced consumption of transfats. Transfats from partially hydrogenated oils may be more unhealthy than those derived from naturally occurring oils.

Cooking media that contain reduced amounts or no transfats may be more expensive than other cooking media. Therefore, it may be economically beneficial to extend the useful life of such cooking media by increasing the frequency of filtering, using such cooking media only for selected food products, or reducing the volume (and size) of the cooking vessel in which such cooking media are used. Nevertheless, cooking media experience a temperature drop during filtering and cooking time may be wasted if the frequently filtered cooking medium must be reheated before cooking may begin again. Moreover, during cooking, food products may absorb a portion of the cooking medium. While such cooking medium absorption may not be a problem when larger cooking vessels are used, the use of smaller cooking vessels may result in noticeable drops in cooking medium volumes and the need to more frequently “top off” the cooking medium. The frequent addition of new cooking medium also may result in a temperature drop in the cooking medium.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for a cooking medium heating system and in particular, such a system comprising a heat transfer tube or an eductor, or both, that overcome these and other shortcomings of the related art. A technical advantage of the present invention is that the heat may be quickly and efficiently transferred from the heat transfer tube to the cooking medium. A further technical advantage of the present invention is that elevated flow rates of combustion gas may be used because the exhaust gases may be effectively and efficiently vented from the heat transfer tube.

According to an embodiment of the present invention, a heat transfer tube for transferring heat generated by combustion to a cooking medium, may comprise: a bottom wall, a pair of side walls, and a top wall. All tube walls may be straight, semi-circular, concave, or convex, or may form an obtuse angle. The tube further may comprise a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof.

In an embodiment, the top wall of the heat transfer tube further may be concave and comprise a first top wall portion and a second top wall portion and the first top wall portion and the second top wall portion intersect to form an obtuse, interior angle. Alternatively, the concave top wall may be arcuate.

The bottom wall may be substantially perpendicular to each of the pair of side walls. Alternatively, the bottom wall may be concave. Further, the pair of side walls may be substantially parallel to each other.

The heat transfer tube also may comprise at least one heat transfer fin extending from proximate to the combustion gas exhaust opening toward the combustion gas entry opening. Alternatively, the at least one heat transfer fin may extend from the combustion gas exhaust opening toward the combustion gas entry opening. In either configuration, the heat transfer fin preferably does not extend to the combustion gas entry opening. The combustion gas is hottest near the entry opening and the fins may not be necessary for quick and efficient heat transfer in this area. The heat transfer fins, however, increase the speed and efficiency of heat transfer as the combustion gas temperature decreases as the flowing combustion gases approach the combustion gas exhaust opening.

A height of the at least one heat transfer fin may decrease as the at least one heat transfer fin approaches the combustion gas entry opening. The increased height of the heat transfer fin may allow the tube to extract more heat from combustion gases having a reducing temperature as the gases approach the combustion gas exhaust opening. The tapered heat transfer fins may allow for more even heat transfer over the length of the tube and may help reduce the likelihood of scorching the cooking medium on the tube's outer surface. Further, the at least one heat transfer fin may comprise a plurality of fin segments. Such a segmented heat transfer fin may have increased strength and may be better able to withstand tube flexing without damage during heating. In addition, the plurality of fin segments of the at least one heat transfer fin may be substantially aligned with a longitudinal axis of the tube.

Consequently, according to another embodiment of the present invention, a heat transfer tube for transferring heat generated by combustion to a cooking medium, may comprise: a bottom wall; a pair of side walls; and a concave top wall. The tube may comprise a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof. A plurality of heat transfer fins may extend from the pair of side walls and the top wall toward the interior of the tube, and each of the plurality of heat transfer fins may extend from proximate to the combustion gas exhaust opening toward the combustion gas entry opening. Each of the plurality of heat transfer fins further may comprise a plurality of fin segments that are substantially aligned with a longitudinal axis of the tube, and a height of each of the plurality of heat transfer fins may decrease as that heat transfer fin approaches the combustion gas entry opening. Alternatively, the heat transfer fins may extend from the bottom wall.

According to still another embodiment of the present invention, a heat transfer tube further may comprise a combustion gas flow separator extending from proximate to the combustion gas exhaust opening toward the combustion gas entry opening and dividing the tube into two spaces between the separator and each of the pair of side walls along a length of the separator. Preferably, the separator is formed from a material that is resistant to the high temperatures encountered in the combustion gas flow and that does not retain heat, e.g., a high-temperature resistant, insulating material. Although the tubes may be made from metal, such as steel, such materials are not suitable for the separator because they would cause heat to be retained within the tubes and slowly released from the separator. Consequently, a preferred separator material is alumina silica or the like.

The separator further may comprise at least one spacer, which contacts at least one of the bottom wall and the pair of side walls to position and limit the movement of the separator within the tube. The separator may have a variety of shapes. Nevertheless, the separator's leading edge, i.e., the edge closest to the combustion gas entry opening, may be configured to direct a flow of combustion gases around the separator and toward at least the pair of side walls. Movement of the separator with the tube, however, is undesirable. Therefore, the tube may comprise a separator positioning abutment disposed proximate to the combustion gas exhaust opening, and the separator further may comprise a separator positioning groove, such that the separator positioning abutment engages the separator positioning groove to limit axial movement of the separator with a flow of combustion gases within the tube.

According to yet another embodiment of the present invention, a combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening of a heat transfer tube, may comprise a flue, a nozzle, and a blower. The flue may be tapered or straight. The flue may comprise a narrower, exhaust gas receiving end disposed adjacent to the combustion gas exhaust opening of the heat transfer tube. The nozzle may comprise a nozzle inlet and a nozzle outlet, wherein the nozzle outlet is disposed within the exhaust gas receiving end of the flue. The blower may be disposed adjacent to the nozzle inlet for delivering a flow of air to the nozzle inlet and thereby creating a venturi effect.

According to a further embodiment of the present invention, a cooking medium heating system may comprise a cooking vessel for holding a cooking medium, at least one heat transfer tube extending through the cooking vessel for transferring heat generated by combustion to the cooking medium, and a combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening of each of the at least one tube. The at least one heat transfer tube may comprise a bottom wall, a pair of side walls, and a concave top wall. Each of the at least one heat transfer tube may comprise a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof. At least one heat transfer fin may extend from proximate to the combustion gas exhaust opening toward the combustion gas entry opening. A combustion gas flow separator may extend from proximate to the combustion gas exhaust opening toward the combustion gas entry opening and dividing the tube into two spaces between the separator and each of the pair of side walls along a length of the separator. The combustion gas eductor may comprise a flue comprising a narrower, exhaust gas receiving end disposed adjacent to the combustion gas exhaust opening of the at least one tube; a nozzle comprising a nozzle inlet and a nozzle outlet, wherein the nozzle outlet is disposed within the exhaust gas receiving end of the flue; and a blower disposed adjacent to the nozzle inlet for delivering a flow of air to the nozzle inlet.

Other objects, features, and advantages of the present invention will be apparent to persons of ordinary skill in the art in view of the foregoing detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings.

FIG. 1A is a broken, plan view of a heat transfer tube component, and FIG. 1B is a perspective view of the heat transfer tube component of FIG. 1A.

FIG. 2A is a side view of the heat transfer tube component of FIG. 1A, and FIG. 2B is a cross-sectional view of heat transfer tube formed from two, joined heat transfer tube components of FIG. 2A.

FIG. 3A is a side view of another configuration of a heat transfer tube component, and FIG. 3B is a cross-sectional view of a heat transfer tube formed from two, joined heat transfer tube components of FIG. 3A.

FIG. 4A is a side view of another configuration of a heat transfer tube component, and FIG. 4B is a cross-sectional view of a heat transfer tube formed from two, joined heat transfer tube components of FIG. 4A.

FIG. 5A is a perspective view of a pair of heat transfer fins, FIG. 5B is a side view of the pair of heat transfer fins of FIG. 5A, and FIG. 5C is a front view of the pair of heat transfer fins of FIG. 5A from the orientation of line V-V.

FIG. 6 is a perspective view of a configuration of a combustion gas flow separator.

FIG. 7 is a perspective view of a trailing edge of a combustion gas flow separator depicting a separator positioning groove.

FIG. 8 is a perspective view of another configuration of a combustion gas flow separator.

FIG. 9 is a perspective view of yet another configuration of a combustion gas flow separator.

FIG. 10 is a perspective view of a further configuration of a combustion gas flow separator.

FIG. 11 is a perspective view of still another configuration of a combustion gas flow separator.

FIG. 12A is a schematic diagram of a combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening of a heat transfer tube, and FIG. 12B is a schematic diagram of the combustion gas eductor depicting the flue.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Preferred embodiments of the present invention, and their features and advantages, may be understood by referring to FIGS. 1A-12B, like numerals being used for corresponding parts in the various drawings.

Referring to FIG. 1A, a broken, plan view of a heat transfer tube component 10 is depicted. Heat transfer tube component 10 comprises a bottom wall 12, a side wall 14, and a top wall 16. FIG. 1B depicts a perspective view of heat transfer tube component 10 of FIG. 1A. As depicted in FIGS. 1A and 1B, bottom wall 12 is substantially perpendicular to side wall 14, and top wall 16 joins side wall 14 at an obtuse angle. Heat transfer tube component 10 may be made from a material capable of withstanding the temperatures of the combustion gases, which has suitable heat transfer properties and which will not react adversely with the cooking medium or the food products. For example, in a preferred embodiment, heat transfer tube component 10 may be made from 304 stainless steel and may have a thickness of about 0.16 cm.

FIG. 2A depicts a side view of heat transfer tube component 10 of FIG. 1A. A heat transfer tube 100 may be formed by joining two heat transfer tube components 10 together by welding or brazing. In FIG. 2B, seams 18 a and 18 b join heat transfer tube components 10. Referring again to FIG. 2B, heat transfer tube 100 comprises a pair of substantially parallel side walls 14. Bottom walls 12 of heat transfer tube components 10 form a bottom wall of heat transfer tube 100, and top walls 16 of heat transfer tube components 10 form a concave top wall of heat transfer tube 100. In particular, top walls 16 intersect to form an obtuse, interior angle A.

FIG. 3A depicts a side view of heat transfer tube component 30, two of which may be joined together to form another configuration of a heat transfer tube. In FIG. 3B, a heat transfer tube 300 may be formed by joining two heat transfer tube components 30 together at seams 38 a and 38 b by welding or brazing. Referring again to FIG. 3B, heat transfer tube 300 comprises a pair of substantially parallel side walls 34. Bottom walls 32 of heat transfer tube components 30 form a bottom wall of heat transfer tube 300, and curved top walls 36 of heat transfer tube components 30 form a concave top wall of heat transfer tube 300. The curved, outer surface of the concave top wall of heat transfer tube 300 prevents food particles and cracklings from resting on the top wall of heat transfer tube 300 and reduces or eliminates scorching of the top wall. Consequently, time expended in cleaning the tubes may be reduced.

FIG. 4A depicts a side view of heat transfer tube component 40. As depicted in FIG. 4A bottom wall 42 is curved, and top wall 46 is curved. Side wall 44 joins top wall 46 to bottom wall 42. Two of heat transfer tube component 40 may be joined together to form another configuration of a heat transfer tube. In FIG. 4B, a heat transfer tube 400 may be formed by joining two heat transfer tube components 40 together at seams 48 a and 48 b by welding or brazing. Referring again to FIG. 4B, curved bottom walls 42 of heat transfer tube components 40 form a concave bottom wall of heat transfer tube 400, and curved top walls 46 of heat transfer tube components 40 form a concave top wall of heat transfer tube 400. The arcuate, outer surface of the concave bottom wall of heat transfer tube 400 may prevent the development of fatigue cracks, thereby extending the service life of the heat transfer tube.

In addition to the fabrication methods described in the preceding paragraphs, heat transfer tubes 100, 300, 400 may also be formed by roll forming tubes with a single weld seam, by extrusion, or by any other suitable method.

As noted above, when using more expensive zero transfat cooking media, it may be economically beneficial to increase the frequency of filtering, to use such cooking media only for selected food products, or to reduce the volume (and size) of the cooking vessel in which such cooking media are used. Nevertheless, when heating or reheating a cooking medium in a smaller cooking vessel, efficient cooking may require that the cooking media is brought to cooking temperature as quickly as possible. Nevertheless, it also is important that the heat transfer tube is heated evenly to reduce or eliminate scorching and uneven cooking. The use of heat transfer fins within the heat transfer tube helps ensure the even transfer of heat from the combustion gases to the walls of the heat transfer tubes.

Referring to FIG. 5A, a perspective view of a pair of heat transfer fins 50 is depicted. In this configuration, the pair of fins 50 are aligned in parallel and are joined by a securing portion 52. The pair of fins 50 may be welded or brazed or otherwise secured to the walls of the heat transfer tube. In a preferred embodiment, the pair of fins 50 is brazed to the interior of the tubes. Brazing may cause less distortion to the tubes and leaves a smooth outer tube surface. Reduced distortion may facilitate the assembly of heat transfer tube components into heat transfer tubes. See FIGS. 2A, 3A, and 4A, supra. Further, welding the fins or the pair of fins 50 to the heat transfer tubes may leave dimples or blemishes on the exterior of the heat transfer tubes. These dimples or blemishes may increase the occurrence of uneven heating and scorching and may increase the need for and frequency of tube cleaning.

Because the combustion gases are hottest at the point at which they enter the heat transfer tube, fins may not be necessary or desirable in the vicinity of the combustion gas entry opening. The presence and length of this set back or fin-free zone in the heat transfer tube may depend on the overall length of the tube, the volume and size of the cooking vessel, the materials from which the tube and fins are manufactured, and the speed with which the cooking medium is to be heated to a desired temperature. In addition, a height of the transfer fin may decrease as the heat transfer fin approaches the combustion gas entry opening. Further, the heat transfer fin may comprise a plurality of fin segments. Such a segmented heat transfer fin may have increased strength and may be better able to withstand tube flexing without damage during heating. Moreover, as depicted in FIG. 5A, the plurality of fin segments of the at least one heat transfer fin may be substantially aligned with a longitudinal axis of the tube.

Referring to FIGS. 5B and 5C, the height of the heat transfer fin may allow the tube to extract more heat from combustion gases having a reduced temperature as the gases approach the combustion gas exhaust opening. In the depicted embodiment, upstream fin segments 54 are initially tapered and downstream fin segments 56 are of a substantially constant height. The total number of fin segments, the ratio of tapered to constant height fin segments, and the degree of tapering and the maximum height of the fin segments may be varied depending upon the parameters of the particular cooking operation. As noted above, tapered fin segments 44 and constant height fin segments 56 may allow for more even heat transfer over the length of the tube and may help reduce the likelihood of scorching the cooking medium on the tube's outer surface. Fins may be made from a material capable of withstanding the temperatures of the combustion gases, having suitable heat transfer properties, and capable of being secured to the heat transfer tubes. For example, in a preferred embodiment, the pair of fins 50 may be made from 304 stainless steel and may have a thickness of about 0.09 cm.

FIG. 6 is a perspective view of a configuration of a combustion gas flow separator 60. As with the pair of fins 50 described above, combustion gas flow separator 60 extends from proximate to the combustion gas exhaust opening toward the combustion gas entry opening and divides the tube into two spaces between separator 60 and each of the pair of side walls along a length of separator 60. Preferably, separator 60 is formed from a material that is resistant to the high temperatures encountered in the combustion gas flow and that does not retain heat, e.g., a high-temperature resistant, insulating material. Consequently, a preferred separator material is alumina silica or the like.

Separator 60 may rest on and may be positioned within the heat transfer tube by the heat transfer fins. Nevertheless, as noted above, the fins may not extend to the combustion gas entry opening. Consequently, separator 60 may comprise at least one spacer 62 which contacts at least one of the pair of side walls (not shown) to position and limit the movement of separator 60 within the tube. The separator may have a variety of shapes. See FIGS. 8, 9, 10, 11 infra. Nevertheless, a leading edge 64, i.e., the edge closest to the combustion gas entry opening, of separator 60 may be configured to direct a flow of combustion gases around separator 60 and toward at least the pair of side walls.

FIG. 7 is a perspective view of a trailing edge of a combustion gas flow separator depicting a separator positioning groove. Although the separator is positioned directly in the combustion gas flow path, movement of the separator within the tube, however, is undesirable. Therefore, the tube may comprise a separator positioning abutment (not shown) disposed proximate to the combustion gas exhaust opening, and the separator further may comprise a separator positioning groove 72, such that the separator positioning abutment engages separator positioning groove 72 to limit axial movement of the separator with a flow of combustion gases within the tube. In FIG. 7, separator positioning groove 72 is depicted at the upper, trailing edge of the separator. Nevertheless, separator positioning groove 72 may be disposed alternatively on either side of the separator or may be disposed at the lower, trailing edge of the separator. Further, although the separator positioning abutment is not depicted, the separator may be any cylindrical, box-like, or finger-like extension from the tube walls, which is shaped and disposed to engage separator positioning groove 72. The separators described in FIG. 6, 8, 9, 10, or 11 also may comprise a separator positioning groove which is engaged by a separator positioning abutment on the tube.

FIG. 8 is a perspective view of another configuration of a combustion gas flow separator 80. Similar to the embodiment of FIG. 6, separator 80 may comprise at least one spacer 82 which contacts at least one of the pair of side walls (not shown) to position and limit the movement of separator 80 within the tube. In FIG. 8, a leading edge 84, i.e., the edge closest to the combustion gas entry opening, of separator 80 may be configured to direct a flow of combustion gases around separator 80 and toward at least the pair of side walls. Further, separator 80 includes a step down 86 a and a step up 86 b to allow the combustion gases to flow more freely under and above separator 80. Such an arrangement may increase contact between the flowing combustion gases and the tube walls and may further enhance heat transfer to the cooking medium. In addition, raised portions 88 a and 88 b remain proximate to or in contact with the top and bottom walls of the heat transfer tube and may secure and support separator 80 within the tube.

FIG. 9 is a perspective view of still another configuration of a combustion gas flow separator 90. Similar to the embodiment of FIG. 6, separator 90 may comprise at least one spacer 92 on the leading edge, i.e., the edge closest to the combustion gas entry opening, which contacts at least one of the pair of side walls (not shown). Further, the leading edge of separator 90 may be bowed or arched in the opposite direction to the combustion gas flow. The at least one spacer 92 positions and limits the movement of separator 90 within the tube. As depicted in FIG. 9, separator 90 further comprises a top protrusion 96 a spaced inwardly from sides 94 of separator 90, and a bottom protrusion 96 b spaced inwardly from sides 94 of separator 90. Top protrusion 96 a and bottom protrusion 96 b aid the flow of combustion gasses around the separator.

FIG. 10 is a perspective view of yet another configuration of a combustion gas flow separator 1000. As shown in FIG. 10, separator 1000 comprises a top protrusion 102 a spaced inwardly from sides 104 of separator 1000, and a bottom protrusion 102 b spaced inwardly from sides 104 of separator 1000. Further, the leading edge of separator 1000 may be curved or rounded to improve the flow of combustion gases around the separator 1000. Nevertheless, in FIG. 10, top protrusion 102 a further includes a step up 106 a to raised portion 108 a, and bottom protrusion 102 b includes a step down 106 b to raised portion 108 b. This configuration permits the combustion gases to flow more freely under and above separator 1000, which may increase contact between the flowing combustion gases and the tube walls and may further enhance heat transfer to the cooking medium. In addition, raised portions 108 a and 108 b remain proximate to or in contact with the top and bottom walls of the heat transfer tube. Such contact may secure and support separator 1000 within the tube.

FIG. 11 is a perspective view of a further configuration of a combustion gas flow separator 1100. Similar to the embodiments of FIGS. 6, 8, and 9, separator 1100 may comprise at least one spacer 112 which contacts at least one of the pair of side walls (not shown) to position and limit the movement of separator 1100 within the tube. In this embodiment, however, spacers 112 are wing-shaped and may interfere less with the flow of combustion gases around separator 1100. Further, a leading edge 114, i.e., the edge closest to the combustion gas entry opening, of separator 1100 may be configured in an even more aerodynamic shape to direct a flow of combustion gases around separator 1100 and toward at least the pair of side walls and to reduce or eliminate turbulence within the tube. Nevertheless, in this embodiment, separator 1100 includes a step down 116 a and a step up 116 b which permit the combustion gases to flow more freely under and above separator 1100. This may increase contact between the flowing combustion gases and the tube walls and may further enhance heat transfer to the cooking medium. In addition, raised portions 118 a and 118 b remain proximate to or in contact with the top and bottom walls of the heat transfer tube and may secure and support separator 1100 within the tube.

FIG. 12A is a schematic diagram of a combustion gas eductor 120 for venting combustion gas EG exhausted from a combustion gas exhaust opening of a heat transfer tube 300. The combustion gas eductor described herein is compatible with each of the heat transfer tubes described herein. Only heat transfer tube 300, however, is shown in FIG. 12A for exemplary purposes. Combustion gas eductor 120 may comprise a flue 122, a nozzle 124, and a blower 126. Flue 122 may be tapered or straight. Referring to FIG. 12B, flue 122 may comprise a narrower, exhaust gas receiving end 123 disposed adjacent to the combustion gas exhaust opening of heat transfer tube 300. Nozzle 124 may comprise a nozzle inlet 125 a and a nozzle outlet 125 b, wherein nozzle outlet 125 b is disposed within exhaust gas receiving end 123 of flue 122. Blower 126 may disposed adjacent to nozzle inlet 125 a for delivering a flow of air AF to nozzle inlet 125 a and thereby creating a venturi effect.

Referring again to FIG. 12A, combustion gas CG enters heat transfer tube 300 through a combustion gas entry opening. After heat from combustion gas CG is transferred to the cooking medium, exhaust gas EG exits heat transfer tube 300 through the combustion gas exhaust opening. An updraft is created by the combination of air flow AF generated by blower 126 passing through nozzle 124 and into flue 122. This updraft draws exhaust gas EG into flue 122 and thereby vents the combustion gas EG exhausted from a combustion gas exhaust opening of a heat transfer tube 300.

While the invention has been described in connection with preferred embodiments, it will be understood by those of ordinary skill in the art that other variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those of ordinary skill in the art from a consideration of the specification or practice of the invention disclosed herein. The specification and the described examples are considered as exemplary only, with the true scope and spirit of the invention indicated by the following claims. 

1. A heat transfer tube for transferring heat generated by combustion to a cooking medium, comprising: a bottom wall; a pair of side walls; a top wall; a combustion gas entry opening and a combustion gas exhaust opening formed at opposite ends of the heat transfer tube; and at least one heat transfer fin extending from a position proximate to the combustion gas exhaust opening toward the combustion gas entry opening.
 2. The heat transfer tube of claim 1, wherein the top wall is concave, each of the pair of side walls is substantially parallel to the other side wall, and the bottom wall is substantially perpendicular to each of the pair of side walls.
 3. The heat transfer tube of claim 2, wherein the top wall further comprises a first top wall portion and a second top wall portion and the first top wall portion and the second top wall portion intersect to form an obtuse, interior angle.
 4. The heat transfer tube of claim 2, wherein the top wall is arcuate.
 5. The heat transfer tube of claim 1, wherein the bottom wall is concave.
 6. The heat transfer tube of claim 1, wherein the at least one heat transfer fin extends from the combustion gas exhaust opening toward the combustion gas entry opening.
 8. The heat transfer tube of claim 1, wherein a height of the at least one heat transfer fin decreases as the at least one heat transfer fin approaches the combustion gas entry opening.
 9. The heat transfer tube of claim 1, wherein the at least one heat transfer fin comprises a plurality of fin segments.
 10. The heat transfer tube of claim 9, wherein the plurality of fin segments of the at least one heat transfer fin are substantially aligned with a longitudinal axis of the heat transfer tube.
 11. The heat transfer tube of claim 9, wherein a height of the at least one heat transfer fin decreases as the at least one heat transfer fin approaches the combustion gas entry opening.
 12. The heat transfer tube of claim 9, wherein a height of the at least one heat transfer fin decreases substantially uniformly as the least one heat transfer fin approaches the combustion gas entry opening.
 13. The heat transfer tube of claim 1, wherein the at least one heat transfer fin extends from one of the pair of side walls.
 14. The heat transfer tube of claim 1, wherein the at least one heat transfer fin extends from the top wall.
 15. The heat transfer tube of claim 1, wherein the at least one heat transfer fin extends from the bottom wall.
 16. A heat transfer tube for transferring heat generated by combustion to a cooking medium, comprising: a bottom wall; a pair of side walls; a top wall, the heat transfer tube comprising a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof; and a plurality of heat transfer fins extends from the pair of side walls and the top wall toward the interior of the heat transfer tube and each of the plurality of heat transfer fins extends from a position proximate to the combustion gas exhaust opening toward the combustion gas entry opening, each of the plurality of heat transfer fins further comprises a plurality of fin segments that are substantially aligned with a longitudinal axis of the heat transfer tube, and a height of each of the plurality of heat transfer fins decreases as that heat transfer fin approaches the combustion gas entry opening.
 17. The heat transfer tube of claim 16, wherein the at least one heat transfer fin extends from one of the pair of side walls.
 18. The heat transfer tube of claim 16, wherein the at least one heat transfer fin extends from the top wall.
 19. The heat transfer tube of claim 16, wherein the at least one heat transfer fin extends from the bottom wall.
 20. The heat transfer tube of claim 1, further comprising a combustion gas flow separator extending from a position proximate to the combustion gas exhaust opening toward the combustion gas entry opening and dividing the heat transfer tube into two spaces between the separator and each of the pair of side walls along a length of the separator.
 21. The heat transfer tube of claim 20, wherein the separator is formed from a high-temperature resistant, insulating material.
 22. The heat transfer tube of claim 21, wherein the high-temperature resistant, insulating material is alumina silica.
 23. The heat transfer tube of claim 20, wherein the separator further comprises at least one spacer, which contacts at least one of the bottom wall and the pair of side walls to position and limit the movement of the separator within the heat transfer tube.
 24. The heat transfer tube of claim 20, wherein the separator further comprises a leading edge configured to direct a flow of combustion gases around the separator and toward at least the pair of side walls.
 25. The heat transfer tube of claim 20, further comprising a separator positioning abutment disposed proximate to the combustion gas exhaust opening and wherein the separator further comprises a separator positioning groove, such that the separator positioning abutment engages the separator positioning groove to limit axial movement of the separator with a flow of combustion gases within the heat transfer tube.
 26. A combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening of a heat transfer tube, comprising: a flue comprising a narrower, exhaust gas receiving end disposed adjacent to the combustion gas exhaust opening of the heat transfer tube; a nozzle comprising a nozzle inlet and a nozzle outlet, wherein the nozzle outlet is disposed within the exhaust gas receiving end of the flue; and a blower disposed adjacent to the nozzle inlet for delivering a flow of air to the nozzle inlet.
 27. A cooking medium heating system comprising: a cooking vessel for holding a cooking medium; at least one heat transfer tube extending through the cooking vessel for transferring heat generated by combustion to the cooking medium, comprising: a bottom wall, a pair of side walls, and a top wall, wherein each of the at least one heat transfer tube comprises a combustion gas entry opening and a combustion gas exhaust opening formed therein at opposite ends thereof; at least one heat transfer fin extending from a position proximate to the combustion gas exhaust opening toward the combustion gas entry opening; a combustion gas flow separator extending from a position proximate to the combustion gas exhaust opening toward the combustion gas entry opening and dividing the heat transfer tube into two spaces between the separator and each of the pair of side walls along a length of the separator; and a combustion gas eductor for venting combustion gas exhausted from a combustion gas exhaust opening of each of the at least one tube, comprising: a flue comprising a narrower, exhaust gas receiving end disposed adjacent to the combustion gas exhaust opening of the at least one tube; a nozzle comprising a nozzle inlet and a nozzle outlet, wherein the nozzle outlet is disposed within the exhaust gas receiving end of the flue; and a blower disposed adjacent to the nozzle inlet for delivering a flow of air to the nozzle inlet. 